The plating of wafers, substrates and other articles involves many parameters that need to be controlled to achieve a desired plating characteristics. These parameters may include the electrostatic field between the anode and the cathode in contact with the article to improve the uniformity of the plating deposition across the surface of the wafer, the ion concentration gradient between the anode and the cathode contact with the article to improve the plating rate, and the placement of the wafer within a plating bath to improve the plating of via holes on the wafer. There are many other parameters that affect the plating characteristic of a wafer.
One particular plating parameter of interest to the invention is the chemical composition of the plating fluid used in plating wafers, substrates, and other articles. A typical plating fluid comprises a mixture of different chemical solutions including de-ionized (DI) water. In order to obtain a desired plating characteristic across the surface of a wafer, the plating fluid should include the proper concentrations of these chemical solutions. If the proper concentrations of these chemical solutions are not present in the plating fluid, the desired plating characteristic across the surface of a wafer may not be achieved. Therefore, it is desired to properly set and maintain the desired concentrations of the chemical solutions in the plating fluid prior to and during the plating of a wafer.
One impediment to maintaining the desired concentrations of the chemical solutions in a plating fluid during the plating cycle is that these concentrations are continuously changing. One reason for this is that the chemical solutions continuously dissipate, decompose, and/or combine with other chemicals during the plating cycle. Thus, the concentrations of the various chemicals in a plating fluid will change with time if the plating fluid is left alone. Accordingly, plating apparatus provide specialized devices to control the concentrations of the chemicals in the plating fluid during the plating cycle.
One such specialized device is a chemical real time analyzer (RTA). An RTA is a device that probes the plating fluid and periodically determines the concentrations of the chemicals in the plating fluid. Using the information of the current concentrations of the chemicals in the plating fluid, the RTA then determines which and amount of chemical solutions that need to be added to the plating fluid and the amount of plating fluid that needs to be drained prior to adding the chemicals in order to achieve the desired concentrations for the chemicals in the plating fluid. This information is used to control a chemical replenishment system that precisely drains the plating fluid reservoir and precisely adds the proper quantities of chemical solutions to the plating fluid to achieve the desired concentrations for the chemicals in the plating fluid. The measuring and replenishing of the plating fluid occurs periodically during a plating cycle.
The invention provides a plating system, a plating chemical replenishment apparatus and method that precisely adds the right quantities of chemical solutions and precisely drains the plating fluid under the control of an RTA to achieve the desired concentrations for the chemicals in the plating fluid.